/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.swak.mmap;

import java.io.IOException;
import java.util.concurrent.atomic.AtomicLong;

public abstract class ReferenceResource {
	protected final AtomicLong refCount = new AtomicLong(1);
	protected volatile boolean available = true;
	protected volatile boolean cleanupOver = false;
	private volatile long firstShutdownTimestamp = 0;

	public synchronized boolean hold() {
		if (this.isAvailable()) {
			if (this.refCount.getAndIncrement() > 0) {
				return true;
			} else {
				this.refCount.getAndDecrement();
			}
		}

		return false;
	}

	public boolean isAvailable() {
		return this.available;
	}

	public void shutdown(final long intervalForcibly) throws IOException{
		if (this.available) {
			this.available = false;
			this.firstShutdownTimestamp = System.currentTimeMillis();
			this.release();
		} else if (this.getRefCount() > 0) {
			if ((System.currentTimeMillis() - this.firstShutdownTimestamp) >= intervalForcibly) {
				this.refCount.set(-1000 - this.getRefCount());
				this.release();
			}
		}
	}

	protected void release() {
		long value = this.refCount.decrementAndGet();
		if (value > 0)
			return;
		synchronized (this) {
			this.cleanupOver = this.cleanup(value);
		}
	}

	public long getRefCount() {
		return this.refCount.get();
	}

	public boolean isCleanupOver() {
		return this.refCount.get() <= 0 && this.cleanupOver;
	}

	/**
	 * shutdown 时 释放资源
	 * 
	 * @param currentRef
	 * @return
	 */
	protected abstract boolean cleanup(final long currentRef);
}
